The present invention is directed to integrated circuits having current sources and, more particularly, to a method of trimming a current source using an on-chip analog-to-digital converter (ADC).
An integrated circuit (IC) often requires precise sources of current for various purpose, such as bias circuits for high performance circuits such as amplifiers, ADCs, phase-locked loop circuits (PLLs) and power management circuits. The process and voltage dispersions inherent in manufacturing ICs may necessitate trimming (permanent adjustment) of the current from the source to a desired value before delivery of the product. Current source trimming can be performed on a tester, such as automatic test equipment (ATE).
If the measurement and trimming are performed by the tester, the test time is prolonged and the tester needs a precision measurement instrument for voltage or current, which adds to test cost. Moreover, external equipment such as a tester performing measurement and trimming requires several pins on the IC, which then may not be usable in normal operation of the IC, increasing unnecessarily the pin count.
An IC often has an ADC on-chip (incorporated in the IC) for various purposes in normal operation of the IC. For example, in a sensor application-specific IC (ASIC), the ADC may be used to digitize an analog signal from a sensor or, in a general purpose microcontroller IC, the ADC may be used for digital control of a motor drive. The on-chip ADC can be used with other elements of the IC to perform self-trimming of the current source by the IC under control of the tester with reduced test time and without requiring a precision measurement instrument for voltage or current. However, on-chip ADCs have gain and offset errors that can affect the measurement and hence the trimming accuracy.
It would be advantageous to have a method of accurately trimming a current source using an imprecise on-chip ADC.